Sometimes we don’t notice transposed letters.

Daily Writing Tips has an interesting post titled “Cna Yuo Raed Tihs?” The idea is that, if the first and last letter of the word are in the right place (or just the first letter of a three-letter word), then you can probably read the word even if all the letters between the first and last are jumbled.

This phenomenon illustrates the importance of careful proofreading—one word at a time. If you accidentally transpose two letters in the middle of a word, then the faster you read the writing, the smaller the chance that you’ll notice the error.

This phenomenon also illustrates why running a spell check is a good idea. Although you shouldn’t rely exclusively on spell check, using it in conjunction with careful human proofreading can’t hurt; more likely it will catch some mistakes that a human proofreader is prone to miss.